The Animal Core Laboratory will provide five services for the projects in the grant: 1) Establishment and maintenance of breeding colonies of mutant mice, mainly immunodeficient, for the projects, 2) Genotyping of mice for either breeding or experimentation, 3) Provision of pups for gene therapy experiments, 4) Establishment of strains of mice with congenic markers to facilitate monitoring of cells following administration of transduced cells, 5) Assistance with health monitoring and care of immunodeficient mice. The Core will be housed within the Animal Care Facility at Childrens Hospital Los Angeles and run under the direction of Dr. Kenneth Weinberg.